For applications in which negative switching voltages are required, appropriate actuation voltages need to be generated for electronic switching devices, such as switching transistors. An NMOS switch requires a voltage range which extends from a negative voltage for ensuring good isolation to a predetermined voltage above this negative switched voltage, in order to permit a low forward resistance for the switching transistor.
Known switching assemblies use circuits which effectively switch digital levels, such as a reference-ground potential as available positive digital supply voltage and a negative voltage supply potential as negative digital supply voltage. The problem with such circuits, however, is that they cannot be used if the potential difference between the positive digital supply voltage and the negative digital supply voltage exceeds the breakdown voltage of the electronic switching devices used, according to their specification. Another drawback of the conventional circuit type is low immunity to interference and unreliable switching operations when too low a digital supply voltage is provided in comparison with the threshold voltage of the switching device used. The aforementioned drawbacks may be removed by providing additional negative supply voltages and by using stepped or cascaded level converters, but this makes the circuit very complex and requires additional negative supply voltages.